add Shuffling Array Elements recipe

Author: phlipper

chapters/arrays/shuffling-array-elements.md

@@ -0,0 +1,23 @@
+---
+layout: recipe
+title: Shuffling Array Elements
+chapter: Arrays
+---
+## Problem
+
+You want to shuffle the elements in an array.
+
+## Solution
+
+The JavaScript Array `sort()` method accepts a custom sort function. We can write a `shuffle()` method to add some convenience.
+
+{% highlight coffeescript %}
+Array::shuffle = -> @sort -> 0.5 - Math.random()
+
+[1..9].shuffle()
+# => [ 3, 1, 5, 6, 4, 8, 2, 9, 7 ]
+{% endhighlight %}
+
+## Discussion
+
+For more background on how this shuffle logic works, see this [discussion at StackOverflow](http://stackoverflow.com/questions/962802/is-it-correct-to-use-javascript-array-sort-method-for-shuffling).